1. Field of the Invention
This invention relates to glass ceramic-to-metal seals and particularly hermetic glass ceramic seals with nickel base alloys.
2. Description of the Prior Art
U.S. Pat. No. 2,392,314 to Dalton discloses glass material for sealing against metal wherein the amount of Li.sub.2 O in the glass composition is only 0.8%.
U.S. Pat. No. 3,220,815 to McMillan et al discloses a devitrified glass having an expansion coefficient of 142.times.10.sup.-7 (col. 5, line 38). This can be used for sealing with Mesmeric steel having a coefficient of 140.times.10.sup.-7. The glass contains ZnO in addition to Li.sub.2 O and SiO.sub.2.
U.S. Pat. No. 3,564,587 to Ellis discloses a complex glass composition suitable for sealing against metal.
Borom et al, "Journal of the American Ceramic Society", Vol. 58, pages 385-391 (Sept.-Oct., 1975) discloses in Table I glass compositions of which the ingredients are similar to those disclosed in the present application, but which are not taught to be useful as sealants. Moreover, this reference, as well as the above discussed references, do not teach the four step heat treatment of such glass compositions as is taught in the present application, so that there is a distinct difference between the crystalline microstructures of the glass ceramic compositions of the present invention and those of the prior art.